Lithography Apparatus and Method

ABSTRACT

In an embodiment, a method includes: heating a byproduct transport ring of an extreme ultraviolet source, the byproduct transport ring disposed beneath vanes of the extreme ultraviolet source; after heating the byproduct transport ring for a first duration, heating the vanes; after heating the vanes, cooling the vanes; and after cooling the vanes for a second duration, cooling the byproduct transport ring.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.63/270,247, filed on Oct. 21, 2021, which application is herebyincorporated herein by reference.

BACKGROUND

With the increasing down-scaling of semiconductor devices, variousprocessing techniques (e.g., photolithography) are adapted to allow forthe manufacture of devices with increasingly smaller dimensions. Forexample, as the density of gates increases, the manufacturing processesof various features in the device (e.g., overlying interconnectfeatures) are adapted to be compatible with the down-scaling of devicefeatures as a whole. However, as semiconductor processes haveincreasingly smaller process windows, the manufacture of these deviceshave approached and even surpassed the theoretical limits ofphotolithography equipment. As semiconductor devices continue to shrink,the spacing desired between elements (i.e., the pitch) of a device isless than the pitch that can be manufactured using traditional opticalmasks and photolithography equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a block diagram of a lithography system, in accordance withsome embodiments.

FIGS. 2A-2B are detailed views of an extreme ultraviolet (EUV) source,in accordance with some embodiments.

FIGS. 3A-3C are views of a portion of a vane structure, in accordancewith some embodiments.

FIG. 4 is a flow chart of a method for operating a lithography system,in accordance with some embodiments.

FIG. 5 is a temperature chart for components of a lithography systemduring a cleaning process, in accordance with some embodiments.

FIG. 6 illustrates experimental data for a lithography system, inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature’s relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

According to various embodiments, a cleaning process is performed toclean plasma generation byproducts from vanes of a lithography system.The cleaning process includes pre-heating lower portions of the vanes toreduce a temperature difference between the lower portions and upperportions of the vanes. Subsequently, the upper and lower portions of thevanes are uniformly heated to melt the byproducts so that the byproductsdrip off the vanes and can be evacuated. Pre-heating lower portions ofthe vanes reduces the time between the upper portions and lower portionsof the vanes reaching a desired temperature for melting the byproducts.Reducing the time between the upper portions and lower portions of thevanes reaching the desired temperature reduces the risk of the meltedplasma generation byproducts re-solidifying and damaging components ofthe lithography system.

FIG. 1 is a block diagram of a lithography system 10, in accordance withsome embodiments. In some embodiments, the lithography system 10 is anextreme ultraviolet (EUV) lithography system operable to performphotolithography by exposing a resist layer of a wafer to EUV light. Thelithography system 10 includes an EUV source 12 for generating EUVlight, an EUV scanner 14 for patterning the EUV light and exposing awafer to the patterned EUV light, and a controller 16 for controllingthe components of the lithography system 10.

The EUV source 12 is operable to generate EUV light 18, such as lighthaving a wavelength in the range of 1 nm to 100 nm, such as a wavelengthof about 13.5 nm. In some embodiments, the EUV source 12 utilizes alaser-produced plasma (LPP) mechanism to generate the EUV light 18. TheEUV source 12 includes a laser generator 20, a droplet generator 22, alight collector 24, a droplet catcher 26, and byproduct extractor 28.

The laser generator 20 is operable to generate a high-intensity laserbeam 32. In some embodiments, the laser generator 20 is a carbon dioxide(CO₂) laser system. However, it should be appreciated that another typeof laser system may be utilized. In some embodiments, the laser beam 32is generated with an average laser power in the range of 20 kW to 40 kW,and at a frequency in the range of 40 kHz to 100 kHz. Any acceptablelaser beam 32 may be generated by the laser generator 20.

The droplet generator 22 is operable to provide droplets of a materialfor generating a plasma. During operation, the droplets are shot acrossthe light collector 24 and towards the droplet catcher 26. The laserbeam 32 from the laser generator 20 is directed toward the droplets asthey are shot across the light collector 24. When the laser beam 32strikes a droplet, the droplet is vaporized, atomized, and ionized suchthat a plasma is generated. The plasma emits EUV light 18. The selectionof the material for the droplets may be made based on a desiredwavelength of the EUV light 18. In some embodiments, the material istin, and the droplet generator 22 may be referred to as a tin dropletgenerator. Because the laser generator 20, the droplet generator 22, andthe droplet catcher 26 work together to generate a plasma, they may becollectively referred to as a plasma generator. The plasma generatorgenerates the plasma above the light collector 24.

The light collector 24 is operable to collect the EUV light 18 emittedwhen a plasma is generated using the plasma generator (e.g., the lasergenerator 20, the droplet generator 22, and the droplet catcher 26).When the droplets are ionized, the resulting EUV light 18 ishomogeneously scattered such that the EUV light 18 is distributed in alldirections. The light collector 24 condenses and focuses the EUV light18 to form a concentrated beam of the EUV light 18 for a subsequentlithography exposure processes.

The droplet catcher 26 is operable to catch unreacted droplets from thedroplet generator 22 for reprocessing. Reprocessing the droplets mayinclude collecting the droplets and returning the collected material tothe droplet generator 22 for generating additional droplets. When thematerial of the droplets is tin, the droplet catcher 26 may be referredto as a tin droplet catcher.

The byproduct extractor 28 is operable to catch and remove byproducts ofthe plasma generation from the EUV source 12. As will be subsequentlydescribed in greater detail, the byproduct extractor 28 is used toperform a cleaning process for removing the byproducts from the EUVsource 12 while avoiding damaging to fragile components of the EUVsource 12 such as the light collector 24.

The EUV scanner 14 is operable to receive the EUV light 18 from the EUVsource 12, pattern the EUV light 18, and expose a resist layer of awafer to a pattern of the EUV light 18. The resist layer of the wafer isformed of a photosensitive material that is sensitive to the EUV light18, and the pattern of the EUV light 18 may subsequently be transferredto the wafer by developing the photosensitive material to form a resistpattern and then etching features in the wafer using the resist patternas an etching mask. The EUV scanner 14 includes an illuminator 34, amask stage 36, projection optics 38, and a wafer stage 40.

The illuminator 34 is operable to direct the EUV light 18 from the EUVsource to the mask stage 36, particularly to a mask secured on the maskstage 36. The illuminator 34 may include reflective optic components,such as a single mirror or a mirror system having multiple mirrors, orrefractive optic components, such as a single lens or a lens systemhaving multiple lenses (zone plates). In some embodiments, theilluminator 34 is operable to adjust the reflective optic components toprovide off-axis illumination (OAI) to the mask stage 36.

The mask stage 36 is operable to secure a mask on which the EUV light 18from the illuminator 34 is impinged. In some embodiments, the mask stage36 includes an electrostatic chuck for securing the mask. The masksecured to the mask stage 36 includes reflective layers. The reflectivelayers are reflective of the EUV light 18, and define a pattern of alayer of an integrated circuit (IC). When the EUV light 18 is impingedon the mask secured to the mask stage 36, the EUV light 18 is reflectedby the reflective layers, and the reflected EUV light 18 has a patternof the mask.

The projection optics 38 are operable to collect the patterned EUV light18 from the mask secured to the mask stage 36, and project the patternedEUV light 18 onto the wafer stage 40, particularly to a wafer secured onthe wafer stage 40. The projection optics 38 may magnify the patternedEUV light 18. In some embodiments, the projection optics 38 magnify thepatterned EUV light 18 with a magnification of less than one, therebyreducing the size of the patterned EUV light 18. The projection optics38 may include refractive or reflective optics.

The wafer stage 40 is operable to secure a wafer on which the patternedEUV light 18 from the projection optics 38 is impinged. In someembodiments, the wafer stage 40 includes an electrostatic chuck forsecuring the wafer. The wafer may be, for example, a semiconductorwafer, such as a silicon wafer or other type of wafer to be patterned.

The controller 16 is connected to the components of the lithographysystem 10, and is operable to control the components of lithographysystem 10. Specifically, the controller 16 is operable to control thelithography system 10 to perform lithography process(es) and to performcleaning process. The controller 16 may be used to store and controlparameters associated with the operation of the EUV source 12 and theEUV scanner 14. The controller 16 may be implemented in either hardwareor software, and the parameters may be hardcoded or input to thecontroller 16 through an input device. For example, the controller 16may include a processor and a non-transitory computer readable storagemedium storing programming for execution by the processor, where theprogramming includes instructions for controlling the components of theEUV source 12. Similarly, the controller 16 may include a circuit suchas an application-specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or the like for controlling thecomponents of the EUV source 12. As will be subsequently described ingreater detail, the cleaning process performed by the controller 16includes controlling the byproduct extractor 28 to catch and removeplasma generation byproducts from the EUV source 12 while avoidingdamaging to fragile components of the EUV source 12.

FIGS. 2A-2B are detailed views of an EUV source 12, in accordance withsome embodiments. FIG. 2A is a schematic diagram of the EUV source 12 inoperation. FIG. 2B is a three-dimensional cutaway view of the EUV source12. Some features have been omitted from the views for illustrationclarity.

The EUV source 12 further includes a window 42 to receive the laser beam32. The window 42 extends through a bottom of the light collector 24.The laser beam 32 is directed through the window 42 from the lasergenerator 20 (see FIG. 1 ). The laser beam 32 is directed from the lasergenerator 20 to the window 42 by a beam delivery system, such as one ormore mirrors which are operable to convey the laser beam 32 byreflecting the laser beam 32 in a desired direction. The window 42includes a suitable material substantially transparent to the laser beam32.

The light collector 24 is designed with a coating material and shape tofunction as a mirror for generated EUV light 18. In some embodiments,the light collector 24 has an ellipsoidal shape. In some embodiments,the outer diameter of the light collector 24 is in the range of 400 mmto 600 mm, and the window 42 has a diameter in the range 30 mm to 150mm. Other shapes and/or sizes may be used for the light collector 24 andthe window 42. In some embodiments, the coating material of the lightcollector 24 includes multiple reflective layers, such as a plurality ofmolybdenum-silicon film pairs (e.g., a layer of molybdenum above orbelow a layer of silicon in each film pair). The light collector 24 mayfurther include a capping layer (such as a layer of ruthenium) coated onthe multiple reflective layers to substantially reflect the EUV light18. In some embodiments, the light collector 24 may further include agrating structure designed to effectively scatter any of the laser beam32 which may reach the surface of the light collector 24. For example, asilicon nitride layer may be coated on the light collector 24 and may bepatterned to have a grating pattern.

The EUV source 12 further includes a lower cone 46 and an intermediatefocus (IF) module 48. The lower cone 46 may include a treated surfacewhich further directs the EUV light 18 to the IF module 48. The IFmodule 48 is operable to provide intermediate focus of the EUV light 18to convey the EUV light 18 to the EUV scanner 14 (see FIG. 1 ). The IFmodule 48 may include, for example, an IF-cap quick-connect module, forproviding the EUV light 18 to a scanner.

As described above, when the laser beam 32 strikes a droplet 44 from thedroplet generator 22, EUV light 18 is generated. The laser beam 32 fromthe laser generator 20 is generated in pulses and is synchronized toenter through the window 42 to strike the droplet 44 when positioned inthe path of the laser beam 32 to receive peak power from the lasergenerator 20. When the laser beam 32 strikes the droplet 44, the droplet44 is vaporized, atomized, and ionized to create a plasma, resulting inEUV radiation and droplet byproducts. The droplet byproducts are createdas a result of the droplet 44 being vaporized or atomized. Thesebyproducts are scattered during generation, such that they would bedistributed on components of the EUV source 12 (e.g., the window 42 andthe lower cone 46) if their generation were unmitigated. As noted above,the droplets 44 may be tin droplets. Tin contaminates on the window 42and the lower cone 46 would reduce the efficiency of the EUV source 12.The byproduct extractor 28 (see FIG. 1 ) is operable to catch thedroplet byproducts when they are generated so that they are notdistributed on the components of the EUV source 12, thereby improvingthe efficiency of the EUV source 12. The byproduct extractor 28 includesa vane structure 62, heater(s) 64, cooler(s) 66, a byproduct transportring 68, a byproduct transport ring 68, a heat shield 70, a drain line74, and a collector 76.

The vane structure 62 includes vanes 80 and a gutter 82. The vanes 80protrude from the sidewalls of the vane structure 62, and extend alongthe sidewalls of the vane structure 62 in a direction parallel todirection in which the EUV light 18 is directed. As will be subsequentlydescribed for FIG. 3C, the vanes 80 may be V-shaped. The gutter 82 isdisposed beneath the vanes 80. The vane structure 62 may be a machinedstructure formed of a metal. During operation, the vanes 80 catch thegenerated droplet byproducts. A cleaning process may be performedbetween lithography process(es) to clean the byproducts distributed onthe vanes 80. As will be subsequently described in greater detail, thevanes 80 are heated during the cleaning process to melt and recovermaterial, such as tin, that collects on the vanes 80 during thelithography process(es). When heated, the byproducts run down the vanes80 and drip into the gutter 82. The light collector 24 is a precisedevice that is expensive to replace, and so contamination of the lightcollector 24 is undesirable. According to various embodiments, thebyproduct extractor 28 performs the cleaning process for removing thedroplet byproducts from the vanes 80 in a manner that increases thechances of the droplet byproducts dripping into the gutter 82 instead ofonto the light collector 24. Damage to the light collector 24 during thecleaning process may thus be avoided, increasing the lifespan of the EUVsource 12.

The heater(s) 64 are disposed around the vanes 80. The heater(s) 64 mayinclude a plurality of heating elements which are periodically disposedaround the vane structure 62, or a single heating element which extendscontinuously around the vane structure 62. In some embodiments, theheater(s) 64 include heater rod(s), such as resistive heating element(s)or the like.

The cooler(s) 66 are disposed around the heater(s) 64. The cooler(s) 66may include a plurality of cooling elements which are periodicallydisposed around the vane structure 62, or a single cooling element whichextends continuously around the vane structure 62. In some embodiments,the cooler(s) 66 include cooling element(s), such as water coolingpipes(s), thermoelectric cooler(s), or the like.

The byproduct transport ring 68 is disposed beneath the vane structure62, and particularly beneath the gutter 82. Thus, the byproducttransport ring 68 is above the light collector 24. In some embodiments,the byproduct transport ring 68 has an annular shape, so that thebyproduct transport ring 68 extends around the bottom footprint of thevane structure 62 while still allowing the EUV light 18 to passtherethrough. As will be subsequently described in greater detail, thebyproduct transport ring 68 is operable to collect byproducts that dripinto the gutter 82 during a cleaning process for the vanes 80, so thatthe byproducts may be transported to the collector 76. To prevent thebyproducts from solidifying during transportation, the byproducttransport ring 68 includes a heater 78 (not separately illustrated),which is operable to heat the byproduct transport ring 68 duringoperation so that the byproducts remain in the liquid phase. Forexample, the heater 78 may be a resistive heating element which extendsaround and through a core of the byproduct transport ring 68.

The heat shield 70 is disposed beneath the byproduct transport ring 68.The heat shield 70 is formed of a material which is resistant to heat,and is operable to protect the underlying components (e.g., the lightcollector 24) from heat when the byproduct transport ring 68 is heated.In some embodiments, the heat shield 70 includes a channel for holdingand supporting the byproduct transport ring 68. The channel in the heatshield 70 has the same shape as the byproduct transport ring 68 (e.g.,an annular shape). Openings 72 in the heat shield 70 and the byproducttransport ring 68 allow the byproducts in the byproduct transport ring68 to drip into a drain line 74 and flow through to the collector 76.

The drain line 74 is operable to carry the byproducts from the byproducttransport ring 68 to the collector 76. The collector 76 is operable tostore the byproducts. The drain line 74 and the collector 76 may beformed of a material which is substantially chemically inert to thebyproducts, such as polyvinyl chloride (PVC) or the like. The drain line74 connects the heat shield 70 to the collector 76, and may extendthrough the openings 72.

Some or all of the components of the EUV source 12 are disposed in aprocessing chamber 50. In some embodiments, the processing chamber 50 ismaintained at a vacuum during processing. Air absorbs some types oflight, and so maintaining the processing chamber 50 at a vacuum mayincrease processing efficiency.

According to various embodiments, a cleaning process for the vanes 80 isperformed between lithography process(es) to remove byproducts from thevanes 80. The cleaning process includes a heating cycle and a coolingcycle. During the heating cycle, the vanes 80 are heated using theheater(s) 64 and the byproduct transport ring 68 so that byproductscollected on the vanes 80 melt and run down the vanes 80. The meltedbyproducts drip into the gutter 82, onto the byproduct transport ring68, and then into the drain line 74 (see FIG. 2A) so that theyultimately flow to the collector 76 (see FIG. 2A). During the coolingcycle, the vanes 80 are cooled using the cooler(s) 66 so that they maybe safely operated again.

FIGS. 3A-3C are views of a portion of a vane structure 62, in accordancewith some embodiments. FIG. 3A is a schematic top-down view of theportion of the vane structure 62. FIG. 3B is a schematic side view ofthe portion of the vane structure 62. FIG. 3C is a three-dimensionalview of the portion of the vane structure 62. Some features have beenomitted from the views for illustration clarity.

The vane structure 62 further includes an attachment structure 84 foreach vane 80. The attachment structure 84 attaches the vane 80 to thesidewall of the vane structure 62 (e.g., to the main structure of thevane structure 62). The attachment structure 84 may include, e.g., ahinge which is physically coupled to the vane 80 and to the sidewall ofthe vane structure 62, such that the vane 80 is operable to swing aroundthe hinge. In some embodiments, the attachment structure 84 furtherincludes a motor for actuating the vane 80 to move it during operation.

In the illustrated embodiment, the heater(s) 64 include a plurality ofheating elements and the cooler(s) 66 include a plurality of coolingelements. Specifically, a heater 64 and a cooler 66 are disposed in eachvane structure 62, such that each vane 80 is capable of beingindividually heated and cooled. For example, the heater 64 for a vane 80may extend along the length of the vane 80, and the cooler 66 for a vane80 may extend along the length of the attachment structure 84. Duringoperation (e.g., a cleaning process), heat is transferred from theheater 64 to the vane 80 during the heating cycle of the cleaningprocess, and heat is transferred from the vane 80 to the cooler 66during the cooling cycle of the cleaning process. In embodiments wherethe cooler 66 is a cooling pipe disposed in the attachment structure 84,heat may be transferred from the vane 80 to the cooler 66 by flowingwater through the cooling pipe such that heat is carried away from theattachment structure 84 and the vane 80 by conduction. As shown in FIG.3C, a vane 80 may be v-shaped (e.g., the sidewalls of the vane 80 form aV), with the heater 64 for the vane 80 disposed in the hollow regionformed by the sidewalls of the vane 80. In such embodiments, heat istransferred from the heater 64 to the vane 80 by radiation orconvection.

As noted above, a cleaning process is performed to remove byproductsfrom the vanes 80. The heater(s) 64 are used to heat the vanes 80 duringthe cleaning process, and provide substantially uniform heating.However, heat is generated during lithography process(es), and most ofthe generated heat is applied on the top of the vane structure 62 andthe lower cone 46 (see FIG. 2B). Thus, during lithography process(es)and at the beginning of the cleaning process, the upper portions 80U ofthe vanes 80 are warmer than the lower portions 80L of the vanes 80. Asa result, if only the heater(s) 64 were used to heat the vanes 80, theupper portions 80U of the vanes 80 would reach a desired temperaturebefore the lower portions 80L of the vanes 80. The temperature of theupper portions 80U of the vanes 80 (also referred to as the uppertemperature of the vanes 80) would thus be greater than the meltingpoint of the byproducts, while the temperature of the lower portions 80Lof the vanes 80 (also referred to as the lower temperature of the vanes80) would still be below the freezing point of the byproducts. Accordingto various embodiments, the byproduct transport ring 68 is also heatedduring the heating cycle of the cleaning process, and is heated beforethe heater(s) 64 are turned on. Because the byproduct transport ring 68is disposed beneath the vanes 80, heating the byproduct transport ring68 heats the lower portions 80L of the vanes 80. Specifically, heat istransferred from the byproduct transport ring 68 to the vane 80 byradiation, convection, or conduction. The amount of heating performedusing the byproduct transport ring 68 is controlled to reduce thetemperature difference between the upper portions 80U and lower portions80L of the vanes 80 before the heater(s) 64 are used to heat the vanes80. The byproduct transport ring 68 and the heater(s) 64 may then bothbe used to heat the vanes 80, allowing the vanes 80 to be heated moreuniformly, thereby reducing the time between the upper portions 80U andlower portions 80L of the vanes 80 reaching a desired temperature (e.g.,the melting point of the byproducts). More uniformly heating the vanes80 advantageously reduces the amount of time when melted byproductscould run down the upper portions 80U of the vanes 80 and re-solidifyupon reaching the lower portions 80L of the vanes 80. Re-solidifying ofbyproducts on the lower portions 80L of the vanes 80 would lead tomerging and accumulation of the byproducts, eventually resulting in theaccumulated byproducts detaching from the lower portions 80L of thevanes 80, potentially falling onto and damaging the light collector 24(see FIGS. 2A-2B). More uniformly heating the vanes 80 during thecleaning process can reduce the risk of damage to the light collector24, increasing the lifespan of the EUV source 12.

FIG. 4 is a flow chart of a method 400 for operating the lithographysystem 10, in accordance with some embodiments. The method 400 may beperformed by, e.g., the controller 16 (see FIG. 1 ). The controller 16may perform the method 400 by controlling the components of thelithography system 10, and so the components described for FIG. 1 -3Care referred to when describing the method 400.

In step 402, one or more lithography process(es) are performed toprocess one or more semiconductor wafer(s). The lithography process(es)are performed by securing a wafer on the wafer stage 40, and by securinga mask for the wafer on the mask stage 36. The EUV light 18 is thengenerated using the EUV source 12, and scanned on the wafer using theEUV scanner 14. The wafer is coated with a resist layer sensitive to theEUV light 18. The resist layer may be formed of a positive tone resistor a negative tone resist. The resist layer may be a photoresist, whichmay be formed on the target substrate by spin-on coating, soft baking,or combinations thereof. The wafer processing may be repeated as manytimes as desired. During the lithography process(es), the temperature ofthe vanes 80 is below a predetermined value. The predetermined value isless than or equal to the melting point of the plasma generationbyproducts, so that any byproducts which accumulate on the vanes 80during the lithography process(es) remain solid and do not melt. Forexample, when the droplets 44 are tin, the temperature of the vanes 80is below the melting point of tin. In some embodiments, thepredetermined value is 140° C.

In step 404, a cleaning process is performed to clean byproducts fromthe EUV source 12. The cleaning process includes heating the vanes 80 ofthe vane structure 62 until the byproducts on the vanes 80 melt, andthen evacuating the melted byproducts from the vane structure 62 (e.g.,from the processing chamber 50). Heating the vanes 80 includespre-heating the lower portions 80L of the vanes 80 using the byproducttransport ring 68, and subsequently heating the upper portions 80U andlower portions 80L of the vanes 80 together using the heater(s) 64. Theupper portions 80U of the vanes 80 are not heated (or are heated lessthan the lower portions 80L of the vanes 80) during the pre-heating.During the cleaning process, the temperature of the vanes 80 is abovethe predetermined value described for step 402. The vanes 80 are thencooled, and the heating/cooling cycles are repeated a desired quantityof times. Each of these steps will be described in greater detail. Afterthe cleaning process, the lithography process(es) may be performedagain.

In step 406, the byproduct transport ring 68 is heated. The byproducttransport ring 68 may be heated by turning on the heater (not separatelyillustrated) inside the byproduct transport ring 68. For example, whenthe byproduct transport ring 68 includes a heater 78, such as aresistive heating element, the byproduct transport ring 68 may be heatedby providing current to the resistive heating element. The byproducttransport ring 68 is heated for a predetermined duration, until it is apredetermined temperature. In some embodiments, the byproduct transportring 68 is heated for a duration in the range of 3 hours to 4 hours,until it is at a temperature in the range of 100° C. to 500° C. Heatingthe byproduct transport ring 68 to a temperature of less than 100° C.may cause the formation of tin wool. Other acceptable durations ortemperatures may be utilized when heating the byproduct transport ring68. As noted above, heat is transferred from the byproduct transportring 68 to the lower portions 80L of the vanes 80. As such, heating thebyproduct transport ring 68 results in heating of the lower portions 80Lof the vanes 80. Thus, heating the byproduct transport ring 68 reducesthe temperature difference between the upper portions 80U and lowerportions 80L of the vanes 80. Both the byproduct transport ring 68 andthe lower portions 80L of the vanes 80 are heated to a temperature thatis less than the melting point of the byproducts on the vanes 80 duringpre-heating, such that the byproducts are not melted when reducing thetemperature difference between the upper portions 80U and lower portions80L of the vanes 80.

In some embodiments, the byproduct transport ring 68 is heated at asingle continuous heating rate. For example, the heater 78 of thebyproduct transport ring 68 may maintained at a fixed temperature, whichcauses the byproduct transport ring 68 to be heated at a continuousheating rate. When the heater 78 is a resistive heating element, it maybe maintained at a fixed temperature by providing a constant current tothe resistive heating element. In some embodiments, the heater 78 of thebyproduct transport ring 68 is maintained at a temperature in the rangeof 100° C. to 600° C., thereby causing the byproduct transport ring 68to heat at a rate in the range of 60° C./hour to 500° C./hour.

In some embodiments, the byproduct transport ring 68 is heated atmultiple heating rates of increasing value. For example, the heater 78of the byproduct transport ring 68 may be heated with a heating gradientthat increases. When the heater 78 is a resistive heating element, itmay be heated with a heating gradient by providing an increasing to theresistive heating element. In some embodiments, the heater 78 of thebyproduct transport ring 68 is gradually increased from an initialtemperature in the range of 100° C. to 200° C., to a final temperaturein the range of 200° C. to 500° C.

In step 408, the vanes 80 are heated. The vanes 80 may be heated byturning on the heater(s) 64 and turning off the cooler(s) 66 (if theyare on). For example, when the heater(s) 64 are resistive heatingelement(s), the heater(s) 64 may be heated by providing current to theresistive heating element. The vanes 80 are heated for a predeterminedduration, until they are a predetermined temperature. In someembodiments, the vanes 80 are heated for a duration in the range of 1hours to 2 hours, until the upper portions 80U of the vanes 80 are at atemperature in the range of 200° C. to 350° C. and until the lowerportions 80L of the vanes 80 are at a temperature in the range of 150°C. to 350° C. Heating the vanes 80 to a temperature of less than 100° C.may cause the formation of tin wool. Other acceptable durations ortemperatures may be utilized when heating the vanes 80. The lowerportions 80L of the vanes 80 may be heated to a lower temperature thanthe upper portions 80U of the vanes 80. Both the upper portions 80U andlower portions 80L of the vanes 80 are heated to a temperature that isgreater than the melting point of the byproducts on the vanes 80.

The heating of the vanes 80 does not begin until after the byproducttransport ring 68 has heated for a desired duration. Specifically, await is performed between the heating of the byproduct transport ring 68and the heating of the vanes 80, such that the byproduct transport ring68 is heated for a predetermined duration before the heating of thevanes 80 begins. In some embodiments, the byproduct transport ring 68 isheated for a duration in the range of 0.5 hours to 1.0 hour beforebeginning the heating of the vanes 80. Other acceptable wait times maybe utilized. As a result, the byproduct transport ring 68 is pre-heatedfor a first duration of time, and then the vanes 80 and the byproducttransport ring 68 are heated together for a second duration of time.Thus, the temperature difference between the upper portions 80U andlower portions 80L of the vanes 80 is reduced before the vanes 80 areheated by the heater(s) 64.

In step 410, the vanes 80 are cooled. The vanes 80 may be cooled byturning off the heater(s) 64 and turning on the cooler(s) 66. Forexample, when the cooler(s) 66 are water cooling pipes(s), the cooler(s)66 may be cooled by flowing water through the cooling pipe(s). The vanes80 are cooled for a predetermined duration, until they are apredetermined temperature. In some embodiments, the vanes 80 are cooledfor a duration in the range of 0.2 hours to 0.5 hours, until the upperportions 80U of the vanes 80 are at a temperature in the range of 100°C. to 300° C. and until the lower portions 80L of the vanes 80 are at atemperature in the range of 100° C. to 200° C. Cooling the vanes 80 to atemperature of less than 100° C. may cause the formation of tin wool.Other acceptable durations or temperatures may be utilized when coolingthe vanes 80. Both the upper portions 80U and lower portions 80L of thevanes 80 are cooled to a temperature that is less than the melting pointof subsequently formed plasma generation byproducts.

In step 412, the byproduct transport ring 68 is cooled. The byproducttransport ring 68 may be cooled by turning off the heater (notseparately illustrated) inside the byproduct transport ring 68. Thus,the lower portions 80L of the vanes 80 are cooled alone, without coolingthe upper portions 80U of the vanes 80. The byproduct transport ring 68is cooled for a predetermined duration, until it is a predeterminedtemperature. In some embodiments, the byproduct transport ring 68 iscooled for a duration in the range of 0.1 hours to 0.3 hours, until itis at a temperature in the range of 100° C. to 300° C. Cooling thebyproduct transport ring 68 to a temperature of less than 100° C. maycause the formation of tin wool. Other acceptable durations ortemperatures may be utilized when cooling the byproduct transport ring68. The byproduct transport ring 68 is cooled to a temperature that isless than the melting point of subsequently formed plasma generationbyproducts.

The cooling of the byproduct transport ring 68 does not begin untilafter the vanes 80 have cooled for a desired duration. Specifically, await is performed between the cooling of the vanes 80 and the cooling ofthe byproduct transport ring 68, such that the vanes 80 are cooled for apredetermined duration before the cooling of the byproduct transportring 68 begins. In some embodiments, the vanes 80 are cooled for aduration in the range of 0.5 hours to 1.0 hour before beginning thecooling of the byproduct transport ring 68. Other acceptable wait timesmay be utilized. As a result, the vanes 80 are pre-cooled for a firstdesired duration, and then the byproduct transport ring 68 is cooled fora second desired duration.

After the vanes 80 have cooled, the heating and cooling cycles may berepeated a desired quantity of times. Each cycle of heating and coolingis referred to as a thermal cycle. In some embodiments, about ⅚ of athermal cycle is spent performing cooling and about ⅙ of a thermal cycleis spent performing heating. Any desired amount of heating and coolingmay be performed for each thermal cycle. Utilizing shorter thermalcycles may be more costly, but reduces the risk of damage to the lightcollector 24.

FIG. 5 is a temperature chart for the components of the lithographysystem during a cleaning process, in accordance with some embodiments.Temperature of the components is plotted against time. As shown, thetemperature of the upper portions 80U and lower portions 80L of thevanes 80 exceeds the melting point T_(M) of the byproducts at timest_(1U) and t_(1L), respectively. As a result of pre-heating thebyproduct transport ring 68, the difference Δt₁ between the times t_(1U)and t_(1L) is reduced. In some embodiments, the time difference Δt₁ isin the range of 5 minutes to 30 minutes. Reducing the time differenceΔt₁ reduces the risk of damage to the light collector 24 during thecleaning process. As further shown, the temperature of the upperportions 80U and lower portions 80L of the vanes 80 falls below themelting point T_(M) of the byproducts at times t_(2U) and t_(2L),respectively. As a result of pre-cooling the vanes 80, the differenceΔt₂ between the times t_(2U) and t_(2L) is reduced. In some embodiments,the time difference Δt₂ is in the range of 15 minutes to 60 minutes.Reducing the time difference Δt₂ reduces the risk of damage to the lightcollector 24 during the cleaning process. FIG. 6 illustratesexperimental data for a lithography system, in accordance with someembodiments. As can be seen, the risk of damage to the light collector24 decreased with decreasing values of the sum of Δt₁ and Δt₂.

Embodiments may achieve advantages. Pre-heating the byproduct transportring 68 during the heating cycle of the cleaning process reduces thetemperature difference between the upper portions 80U and lower portions80L of the vanes 80. This reduces the time between the upper portions80U and lower portions 80L of the vanes 80 reaching a desiredtemperature (e.g., the melting point of plasma generation byproducts)when the vanes 80 are subsequently heated during the heating cycle ofthe cleaning process. Reducing the time between the upper portions 80Uand lower portions 80L of the vanes 80 reaching the desired temperaturereduces the risk of the plasma generation byproducts re-solidifying andfalling on the light collector 24 during the cleaning process. Thelifespan of the EUV source 12 may thus be increased. In an experiment,the availability of a lithography system was improved by from 20% to40%, the maintenance time for the lithography system was reduced to bein the range of 24 hours to 48 hours, and the lifespan of the lightcollector 24 was increased to be in the range of 20 days to 45 days.

The advanced lithography process, method, and materials described abovecan be used in many applications, including fin-type field effecttransistors (FinFETs). For example, the fins may be patterned to producea relatively close spacing between features, for which the abovedisclosure is well suited. In addition, spacers used in forming fins ofFinFETs, also referred to as mandrels, can be processed according to theabove disclosure.

In an embodiment, a method includes: heating a byproduct transport ringof an extreme ultraviolet source, the byproduct transport ring disposedbeneath vanes of the extreme ultraviolet source; after heating thebyproduct transport ring for a first duration, heating the vanes; afterheating the vanes, cooling the vanes; and after cooling the vanes for asecond duration, cooling the byproduct transport ring. In someembodiments of the method, heating the byproduct transport ring reducesa temperature difference between upper portions of the vanes and lowerportions of the vanes. In some embodiments of the method, heating thebyproduct transport ring includes heating the byproduct transport ringat a single continuous heating rate. In some embodiments of the method,heating the byproduct transport ring includes heating the byproducttransport ring at multiple heating rates of increasing value. In someembodiments, the method further includes: generating a plasma with theextreme ultraviolet source, a byproduct of the plasma being distributedon the vanes during generation of the plasma, where the byproducttransport ring is heated to a first temperature, the first temperatureless than a melting point of the byproduct, and where the vanes areheated to a second temperature, the second temperature greater than themelting point of the byproduct. In some embodiments of the method,generating the plasma includes: generating a droplet of a material; andstriking the droplet with a laser beam, the droplet being vaporized,atomized, and ionized to create the plasma. In some embodiments of themethod, the material is tin. In some embodiments of the method, thefirst duration is in a range of 0.5 hours to 1.0 hour and the secondduration is in a range of 0.5 hours to 1.0 hour.

In an embodiment, a method includes: generating a plasma in a processingchamber by striking a tin droplet with a laser beam, a byproduct of thetin droplet distributed on a vane in the processing chamber, an uppertemperature of an upper portion of the vane being greater than a lowertemperature of a lower portion of the vane during generation of theplasma; reducing a difference between the upper temperature and thelower temperature by heating the lower portion of the vane; afterreducing the difference between the upper temperature and the lowertemperature, melting the byproduct of the tin droplet on the vane byheating the upper portion of the vane and the lower portion of the vane;and evacuating the melted byproduct of the tin droplet from theprocessing chamber. In some embodiments of the method, heating the lowerportion of the vane includes: heating a byproduct transport ringdisposed beneath the vane. In some embodiments of the method, heatingthe byproduct transport ring includes: providing a constant current to aheating element of the byproduct transport ring. In some embodiments ofthe method, heating the byproduct transport ring includes: providing anincreasing current to a heating element of the byproduct transport ring.In some embodiments of the method, the byproduct of the tin droplet isnot melted during the reducing the difference between the uppertemperature and the lower temperature. In some embodiments of themethod, heating the upper portion of the vane and the lower portion ofthe vane includes: turning on a heating element, the heating elementextending along a length of the vane. In some embodiments, the methodfurther includes: after evacuating the byproduct of the tin droplet fromthe processing chamber, cooling the upper portion of the vane and thelower portion of the vane; and after cooling the upper portion of thevane and the lower portion of the vane, cooling the lower portion of thevane without cooling the upper portion of the vane.

In an embodiment, an apparatus includes: a plasma generator; a lightcollector; a byproduct transport ring above the light collector, thebyproduct transport ring including a first heating element; a vane abovethe byproduct transport ring; a second heating element extending along alength of the vane; a controller configured to: generate a plasma abovethe light collector with the plasma generator, a plasma generationbyproduct distributed on the vane; heat the first heating element of thebyproduct transport ring to reduce a temperature difference between anupper portion and a lower portion of the vane; and after reducing thetemperature difference, heat the second heating element to melt theplasma generation byproduct distributed on the vane. In someembodiments, the apparatus further includes: a drain line extendingthrough an opening in the byproduct transport ring; and a collectorconnected to the drain line, the plasma generation byproduct beingevacuated to the collector through the drain line when melted. In someembodiments, the apparatus further includes: a heat shield having achannel holding the byproduct transport ring, the drain line extendingthrough an opening in the heat shield. In some embodiments of theapparatus, the plasma generator includes: a droplet generator configuredto provide droplets of a material; a laser generator configured togenerate a laser beam that ionizes the droplets of the material togenerate the plasma; and a droplet catcher configured to catch unreacteddroplets of the material from the droplet generator. In someembodiments, the apparatus further includes: a cooling element, wherethe controller is further configured to: after melting the plasmageneration byproduct distributed on the vane, flow water through thecooling element to cool the vane; and after cooling the vane, coolingthe byproduct transport ring.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: heating a byproducttransport ring of an extreme ultraviolet source, the byproduct transportring disposed beneath vanes of the extreme ultraviolet source; afterheating the byproduct transport ring for a first duration, heating thevanes; after heating the vanes, cooling the vanes; and after cooling thevanes for a second duration, cooling the byproduct transport ring. 2.The method of claim 1, wherein heating the byproduct transport ringreduces a temperature difference between upper portions of the vanes andlower portions of the vanes.
 3. The method of claim 1, wherein heatingthe byproduct transport ring comprises heating the byproduct transportring at a single continuous heating rate.
 4. The method of claim 1,wherein heating the byproduct transport ring comprises heating thebyproduct transport ring at multiple heating rates of increasing value.5. The method of claim 1 further comprising: generating a plasma withthe extreme ultraviolet source, a byproduct of the plasma beingdistributed on the vanes during generation of the plasma, wherein thebyproduct transport ring is heated to a first temperature, the firsttemperature less than a melting point of the byproduct, and wherein thevanes are heated to a second temperature, the second temperature greaterthan the melting point of the byproduct.
 6. The method of claim 5,wherein generating the plasma comprises: generating a droplet of amaterial; and striking the droplet with a laser beam, the droplet beingvaporized, atomized, and ionized to create the plasma.
 7. The method ofclaim 6, wherein the material is tin.
 8. The method of claim 1, whereinthe first duration is in a range of 0.5 hours to 1.0 hour and the secondduration is in a range of 0.5 hours to 1.0 hour.
 9. A method comprising:generating a plasma in a processing chamber by striking a tin dropletwith a laser beam, a byproduct of the tin droplet distributed on a vanein the processing chamber, an upper temperature of an upper portion ofthe vane being greater than a lower temperature of a lower portion ofthe vane during generation of the plasma; reducing a difference betweenthe upper temperature and the lower temperature by heating the lowerportion of the vane; after reducing the difference between the uppertemperature and the lower temperature, melting the byproduct of the tindroplet on the vane by heating the upper portion of the vane and thelower portion of the vane; and evacuating the melted byproduct of thetin droplet from the processing chamber.
 10. The method of claim 9,wherein heating the lower portion of the vane comprises: heating abyproduct transport ring disposed beneath the vane.
 11. The method ofclaim 10, wherein heating the byproduct transport ring comprises:providing a constant current to a heating element of the byproducttransport ring.
 12. The method of claim 10, wherein heating thebyproduct transport ring comprises: providing an increasing current to aheating element of the byproduct transport ring.
 13. The method of claim9, wherein the byproduct of the tin droplet is not melted during thereducing the difference between the upper temperature and the lowertemperature.
 14. The method of claim 9, wherein heating the upperportion of the vane and the lower portion of the vane comprises: turningon a heating element, the heating element extending along a length ofthe vane.
 15. The method of claim 9 further comprising: after evacuatingthe byproduct of the tin droplet from the processing chamber, coolingthe upper portion of the vane and the lower portion of the vane; andafter cooling the upper portion of the vane and the lower portion of thevane, cooling the lower portion of the vane without cooling the upperportion of the vane.
 16. An apparatus comprising: a plasma generator; alight collector; a byproduct transport ring above the light collector,the byproduct transport ring comprising a first heating element; a vaneabove the byproduct transport ring; a second heating element extendingalong a length of the vane; a controller configured to: generate aplasma above the light collector with the plasma generator, a plasmageneration byproduct distributed on the vane; heat the first heatingelement of the byproduct transport ring to reduce a temperaturedifference between an upper portion and a lower portion of the vane; andafter reducing the temperature difference, heat the second heatingelement to melt the plasma generation byproduct distributed on the vane.17. The apparatus of claim 16 further comprising: a drain line extendingthrough an opening in the byproduct transport ring; and a collectorconnected to the drain line, the plasma generation byproduct beingevacuated to the collector through the drain line when melted.
 18. Theapparatus of claim 17 further comprising: a heat shield having a channelholding the byproduct transport ring, the drain line extending throughan opening in the heat shield.
 19. The apparatus of claim 16, whereinthe plasma generator comprises: a droplet generator configured toprovide droplets of a material; a laser generator configured to generatea laser beam that ionizes the droplets of the material to generate theplasma; and a droplet catcher configured to catch unreacted droplets ofthe material from the droplet generator.
 20. The apparatus of claim 16further comprising: a cooling element, wherein the controller is furtherconfigured to: after melting the plasma generation byproduct distributedon the vane, flow water through the cooling element to cool the vane;and after cooling the vane, cooling the byproduct transport ring.